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Fundamental and Applied AgricultureVol. 5(2), pp. 176–187: 2020
doi: 10.5455/faa.82652
AgronomyORIGINAL ARTICLE
Agronomic characterization of soybean and bambaragroundnut genotypes grown on different soils of Lake VictoriaBasin
Benson O Onyango1, Fredrick Otieno Ogolla2*
1Department of Biological Sciences, Jaramogi Oginga Odinga University of Science and Technology,P.O. Box 210 40601, Bondo, Kenya
2Department of Biological Sciences, Chuka University, P.O. Box 109 60400, Chuka, Kenya
ARTICLE INFORMATION
Article HistorySubmitted: 19 Jan 2020Accepted: 16 Mar 2020First online: 29 Apr 2020
Academic EditorMd Kamal [email protected]
*Corresponding AuthorFredrick Otieno [email protected]
ABSTRACT
Neglect and under-utilization of legumes such as soybeans and bambaragroundnuts are the reason for increased food insufficiency in the Lake Vic-toria basin. Diversification of legumes into the cropping systems of LakeVictoria basin ensures protein rich diets and improved soil fertility. Thisstudy was carried out to evaluate agronomic characters of two soybean vari-eties and two bambara groundnut landraces cultivated on different soils ofLake Victoria basin. Seeds of two bambara groundnut landraces; KakamegaCream (KAKC) and Busia Brown (BUSB) were collected from farmers inKakamega and Busia counties, respectively in Kenya. Soil sampling wasdone at selected farmers’ fields with no history of inoculation in Kisumu, PortVictoria, Kendu bay and Karungu within Lake Victoria basin. Screen houseexperiment was performed in plastic pots with two plants of each cultivar.Randomized Complete Block Design was used. Agronomic characters ofBUSB and KAKC landraces differed significant (p<0.05). Bambara ground-nuts performed better in Port Victoria and Kendu bay soils than Kisumuand Karungu. Agronomic performance of two soybean varieties SB19 and‘Safari’ on soils from four sites in Lake Victoria basin was significant (p<0.05).Soybeans yield in Port Victoria and Kendu bay soils was better compared toKisumu and Karungu soils. Agronomic performance of bambara groundnutsand soybeans were influenced by soil type. Port Victoria and Kendu bay soilsresulted in better growth compared to Kisumu and Karungu soils. LandraceKAKC and SB19 had better agronomic performers and are recommended tofarmers and seed companies for certified seed production.
Keywords: Rhizobia, nodulation, soybean, bambara groundnut, landrace
Cite this article: Onyango BO, Ogolla FO. 2020. Agronomic characterization of soybean and bambara groundnutgenotypes grown on different soils of Lake Victoria Basin. Fundamental and Applied Agriculture 5(2): 176–187.doi: 10.5455/faa.82652
1 Introduction
Population in Sub-Saharan Africa may double by 99%by the year 2050 (UNDESA, 2019). Projected rise inpopulation poses challenge of access to food, over-all human welfare and economic growth (FAOSTAT,2017). Concerted efforts such as legume diversifica-tion aimed sustainable food production in Africa arenecessary to ameliorate vulnerability to risks of in-
sufficient food (FAOSTAT, 2017; Stagnari et al., 2017;Muoni et al., 2019). However, inadequate attention,neglect and/or under-utilization of crops such as soy-beans and bambara groundnuts have intensified foodinsufficiency (Oyeyinka et al., 2015; Mubaiwa et al.,2018). Production of legume crops has declined belowpotential yield in regions that include Lake Victoriabasin (Ojiem et al., 2007; Siddique et al., 2011).
Soybean grain has protein (40%), carbohydrate
Onyango and Ogolla Fundam Appl Agric 5(2): 176–187, 2020 177
(30%), digestible fiber (10%) and vitamins. It is alsorich in minerals including Mg, K, Ca, Fe, Cu, Zn,and anti-oxidants (Meghvansi et al., 2010). Produc-tion of soybean in Africa is low due to constrainedsuch as its incompatibility with rhizobia found inAfrican soils (Mpepereki et al., 2000). Further, nodu-lation in soybean vary with cultivars as some culti-vars exclude or restrict nodulation by rhizobia thatbelong to certain sero-groups of Bradyrhizobium spp.(Van Berkum, 2002). However, improved cultivarswith ability to freely nodulate with different membersof rhizobia under natural conditions or inoculationhave been developed by breeding (Mpepereki et al.,2000; Sanginga, 2003). Free natural nodulation al-lows these cultivars to form symbioses with nativerhizobial strains. Nonetheless, Sanginga and Okogun(2003) reported that such promiscuous nodulationdoes not meet the full N demand for the cultivarsnecessitating inoculation. Currently, there is incon-clusive information on the occurrence of indigenoussymbionts of soybeans in soils of parts of Lake Victo-ria basin.
Bambara grain has 20.6% protein, 56.5% carbohy-drate, 6.3% fiber and 6.6% fat (Mazahib et al., 2013).Bambara groundnut has gained prominence as an al-ternative dietary protein source with numerous agro-nomic advantages to smallholder farmers (Azam-Aliet al., 2001; Mkandawire, 2007). However, bambaragroundnuts have no properly established seed sys-tems and sound agronomic practices for adoption(Hillocks et al., 2012; Mubaiwa et al., 2018; Feldmanet al., 2019). Knowledge of Bambara groundnut withoptimal agronomic traits for different soil types re-mains scarce (Stagnari et al., 2017). Given the vari-ation in physicochemical status of the soils of LakeVictoria basin (Jaetzold et al., 2007), selection of bam-bara groundnuts with suitable agronomic charactersin different soils is a necessary step towards improv-ing its production.
2 Materials and Methods
2.1 Study sites
The study was conducted through glasshouse andscreen-house pot experiments, laboratory analysisand on farm trials. The screen-house pot experimentswere carried out at Jaramogi Oginga Odinga Uni-versity of Science and Technology research garden.Soil samples used in pot experiments were collectedfrom farmers’ fields in Port Victoria in Busia County,Kisumu in Kisumu County, Kendu bay in HomabayCounty and Karungu in Migori County in Kenya. Amap of the sites is shown in Fig. 1 and site charac-teristics (Table 1). Chemical analysis of collected soilsamples was done at Kenya Agricultural and Live-stock Research Organization (KALRO) Research lab-oratories in Nairobi. Molecular analysis of rhizobial
isolates was done at the Biosciences East and CentralAfrica (BecA-ILRI Hub). The glasshouse experimentto evaluate symbiotic status of the isolates was doneat Kenya Forestry Research Institute’s headquartersat Muguga, Nairobi. Jaramogi Oginga Odinga Uni-versity of Science and Technology is in Bondo town,Siaya County along Bondo – Usenge road within thelower midland agro-ecological zone characterized byhigh temperatures, low rainfall and high evapora-tion rates (Jaetzold et al., 2007). The University liesbetween longitudes of 31°32′0′′E - 31°57′0′′W and lat-itudes of 0°7′30′′N - 0°10′15′′S of the equator at an al-titude of about 1440 m above sea level (WFAC, 2003).
2.2 Agronomic characterization
Seeds of two bambara groundnut landraces;Kakamega Cream (KAKC) and Busia Brown (BUSB)were collected from farmers in Kakamega and Bu-sia Counties in Kenya, respectively. A prior surveywas done to select the farmer-preferred landraces.Attributes considered during selection included earlymaturity, superior cooking quality and taste. This wasdone to improve the exploitation of farmer held vari-eties with a view of future validation through varietaltesting programmes. The survey involved a question-naire designed to establish the commonly cultivatedand farmer-preferred bambara groundnut varietiesin Kisumu, Siaya, Busia, Vihiga and Kakamega coun-ties. These sites were selected following previousreports by Ambede et al. (2012) and Ngugi (1985) thatthe counties were engaged in bambara groundnutcultivation. Identification of the farmers who partic-ipated in the survey was done randomly, but wasguided by availability of the crop in the homesteadand a history of cultivation. Seeds of two soybeanvarieties (promiscuous SB19 and specific Safari) wereselected for trials based on their host specificity orpromiscuity. Guidance on released soybean lines wasobtained from Kenya Agricultural and Livestock Re-search Organization (Kibos Centre) research officersin charge of legumes. In addition, a field survey wasconducted to determine farmer-preferred soybeanlines in Lake Victoria basin. Certified clean seed mate-rials of SB19 were obtained from Tropical Soil Biologyand Fertility Institute (TSBF), Maseno Centre. Variety‘Safari’ is farmer-held in Lake Victoria basin and wasobtained from farmers in Kakamega County follow-ing the survey. Seed collection was done randomlywith the assistance of TSBF and KALRO extensionofficers, who also helped in varietal identification.Fig. 2 shows the morphology of the seeds of bambaragroundnuts and soybeans used in this study.
2.3 Soil sampling
Soil sampling was done at selected farmers’ fieldswith no history of inoculation in Kisumu, Port Vic-
Onyango and Ogolla Fundam Appl Agric 5(2): 176–187, 2020 178
Figure 1. A map showing four sites within Lake Victoria basin where soil samples used to trap rhizobia wereobtained
Table 1. Soil characteristics of the study sites
Site Site location Agro-climatic zones Soil type
Kisumu 0°6′0′′N, 34°45′0′′E Sub-humid lower midland Clay loamKarungu 0°51′0′′S, 34°8′60′′E Semi-humid lower midland Clay loamKendu bay 0°22′0′′S, 34°38′60′′E Semi-humid lower midland Sandy loamP. Victoria 0°6′0′′N, 33°58′0′′E Sub-humid lower midland Sandy loam
Source: Jaetzold et al. (2007)
Table 2. Chemical composition of soils from the study sites
Soil characterstics Study site
Kendu bay P. Victoria Kisumu Karungu
pH 6.26 6.30 4.10 4.11N (%) 0.17 0.15 0.15 0.14Org. C (%) 1.66 1.51 1.44 1.29P† (ppm) 23.0 19.5 10.0 5.00K (meq %) 0.62 0.56 0.20 0.19Ca (meq %) 3.50 3.95 2.48 1.37Mg (meq %) 7.60 7.85 2.52 2.76Mn (meq%) 0.84 0.61 0.59 0.67Cu (ppm) 1.19 1.04 1.09 1.06Fe (ppm) 14.5 15.98 14.8 18.07Zn (ppm) 6.23 8.46 8.91 6.00Na (meq %) 0.26 0.25 0.07 0.07
All values are the mean of a quadruplicate soil analysis. P† - Available P
Onyango and Ogolla Fundam Appl Agric 5(2): 176–187, 2020 179
Genotype SB19 (Promiscous) Safari (Specific) Kakamega Cream (KAKC) Busia Brown (BUSB)
Size Small Large Large LargeCoat colour Cream Bronze Cream BrownEye colour Brown Brown Grey White
Figure 2. Morphology of soybean varieties and bambara groundnut landraces used in trapping rhizobia andevaluating their symbiotic efficiency
toria, Kendu bay and Karungu within Lake Victoriabasin. The site characteristics are listed in Table 2.At each sampling point, 4 kg of soil was collectedfrom a depth of 5 - 20 cm using a shovel. To avoidcross contamination, the shovel was sprayed in be-tween sampling with 5% sodium hypochlorite solu-tion in a wash bottle, rinsed with water three timesand dried using a sterile cloth. Within each site, fourreplicate samples were collected within an area of 10m2 by randomly sampling four corners. The soilswere placed in brown paper bags and put in bucketcontainers away from sunlight. Each soil sample wasdivided into two lots (1 kg and 3 kg) and used for soilchemical analysis and in glasshouse experiments totrap resident rhizobia using soybeans and bambaragroundnut plants, respectively.
2.4 Chemical analysis of soil samples
Soil samples used in chemical analysis were air dried,crushed using a wooden roller and passed through a0.5 cm mesh to remove any plant or grass fragment.Four hundred grams of the prepared soil samplesin quadruplicates were placed in brown paper bags,tightly sealed and submitted to KALRO’s NationalAgricultural Research Laboratories in Nairobi for soilchemical analysis using the methods described below.
2.4.1 Determination of Soil pH
Soil pH was determined using the CaCl2 method(Thomas, 1996). To a soil sample weighing 10 g, 25mL of 0.01M CaCl2 solution was added. The mixturewas shaken for 30 min. Prior to taking the pH read-ing from a pH meter, the electrode was thoroughlyrinsed to free it of buffer solution. The suspensionwas stirred up and the electrode immersed into thesuspension making sure it did not touch the base ofthe beaker. When the pH reading was stable, thedisplayed value was recorded (McNeal, 1982).
2.4.2 Soil organic carbon
A modified Walkley-Black dry combustion methodwas used to determine the percentage of organic car-bon in the soil samples (Anderson and Ingram, 1994).About 15 g sucrose was dried at 105 °C for 2 hr and11.87 g of this were dissolved in water. The solutionwas made up to 100 mL in a volumetric flask, to makea 50 mg C mL−1 solution. Two and half to 25 mL ofthe solution were pipetted into labelled 100 mL vol-umetric flasks, at 7.5 mL intervals, and made to themark with deionized water. Two milliliters of each ofthese working standards were pipetted into labelled150 mL conical flask and dried at 105 °C in an oven.One gram of air-dried soil sample was weighed intoa 150 mL flask to which 10 mL of 1N K2Cr2O7 wasadded and the contents were gently swirled until thesample was completely wet. This was followed bythe addition of 20 mL of concentrated H2SO4 withfurther swirling to ensure through mixing of the solu-tion in a fume cupboard. After cooling the solution,50 mL of 0.4% BaCl2 was added. The solution was leftto stand over-night and the absorbance of the sam-ples and the standards were read at 600 nm on UVvisible spectrophotometer (Spectronic-20-Bausch andLamb).
2.4.3 Exchangeable cations
Total exchangeable cations were determined follow-ing extraction using 1M acidified ammonium acetate(Lindsay and Norvell, 1978). Air-dried soil samplesweighing 10 g were put in 150 mL plastic containers towhich 40 mL of ammonium acetate were added. Thecontainers were tightly closed and put on a reciprocat-ing shaker (Stuart Flask model) for 1 hr. The solutionwas then filtered through a Whatman number 125 fil-ter paper into 250 mL flasks. The remaining soil waswashed using ammonium acetate making the volumein the collecting flask to about 90 mL. Fresh ammo-nium acetate was used to raise the mark to 100 mL. Af-ter leaching the bases, potassium (K) and sodium (Na)emission were read on a flame spectrophotometer
Onyango and Ogolla Fundam Appl Agric 5(2): 176–187, 2020 180
with the filter set on either K or Na while magnesium(Mg), manganese (Mn) and calcium (Ca) absorptionwere read on an atomic absorption spectrophotome-ter (AAS) model SpectrAA50 using the respectivelamps (Thomas, 1982). The resultant values were con-verted into percentage milli-eqivalents (meq %) per10 g using a conversion table.
2.4.4 Available phosphorus
Soil available P was measured using the Olsenmethod (Olsen, 1954). An air-dried soil sample weigh-ing 2.5 g was placed into a 250 mL polythene shakingbottle followed by addition of Olsen’s extracting so-lution (0.5 M NaHCO3 at pH 8.5). The mixture wasput on a shaker for 30 min and the suspension fil-tered through Whatman No. 42. Five mL of 0.8 Mboric acid and 10 mL of ascorbic acid reagent wereadded and allowed to stand for 1 hr. The P contentwas determined colorimetrically from a phosphorusmolybdate complex formed by addition of acidifiedammonium molybdate (Okalebo et al., 2002).
2.4.5 Total nitrogen
Total soil N was determined using the semi-Kjeldhalmethod (Anderson and Ingram, 1994). Soil sampleswere digested using a digestion solution made up ofselenium powder (being the catalysts), lithium sul-phate and concentrated sulphuric acid. An air-driedsoil sample weighing 0.5 g (0.1 g for ground plantmaterial) was weighed into a digestion tube followedby addition of 4.4 mL of the digested samples. Theresultant mixture was placed on a digester at 360 °Cfor 2 hr. Three reagent blanks were included to eachbatch of the samples. The solution was allowed tocool and 25 mL of distilled water added. A further75 mL of distilled water was added and the solutionwas allowed to settle. Standards were prepared byoven drying 7 g of ammonium sulphate [(NH4)2SO4]at 105 °C for 2 hrs. About 4.714 g of dry ammoniumsulphate was dissolved in 1000 mL of deionized wa-ter (1000 mg N L−1) and 50 mL of the solution waspipetted into a 500 mL volumetric flask. Two anda half milliliters of the digested blank was added toeach flask before marking it, to the mark with dis-tilled water. To 0.1 mL of the sample or standard so-lution, 5 mL of reagent N1 (34 g sodium salicylate, 25g sodium citrate and 0.12 g sodium nitroprusside dis-solved 1000 mL de-ionized water) was added. After15 min, 5 mL of reagent N2 (30 g NaOH, 750 mL waterand 10 mL sodium hypochlorite in 240 mL de-ionizedwater) was added. The solution was mixed well andleft for colour development. Total N in the samplewas determined calorimetrically from the clear solu-tion against a set of standards at an absorbance of 655nm.
2.5 Screen-house experiments
The soil samples were used to evaluate agronomicperformance of soybean and bambara groundnut cul-tivars through a screen-house experiment. Plasticpots (20 cm diameter and 25 cm height) were filledwith soil samples and watered until adequately wet.Four seeds of each cultivar were planted on eachpot but were later thinned to two. The set-up wasarranged in Randomized Complete Block Design(RCBD) with four soil types, two soybean varietiesor two bambara groundnut landraces each replicatedfour times. Watering was done twice a day in themorning and evening. The data collected were; Emer-gence days after sowing (EDAS), days to first flow-ering (DFF), days after sowing (DAS), leaf number(LNo 14, 54 and 70 DAS), number of nodules perplant (NodP 21 and 54 DAS), plant height (PHT, cm,14, 54 and 70 DAS), days to maturity (DTM), numberof seeds per pod (SPD), number of pods per plant(NoPd) and weight of 100 seeds (WHS, g). Exper-iments data were organized into a matrix and sub-jected to two- and three-way analysis of variance us-ing Genstat 16th Edition and significant means sep-arated using Least Significant Difference [at LSD5%]and Dancun Multiple Range Test.
3 Results
3.1 Soil analysis
Differences in chemical properties of soil samplesfrom the four study sites were as shown in Table 2.Soil samples from Kendu bay and Port Victoria werenear neutral with pH ranging from 6.26 – 6.30, un-like Karungu and Kisumu which had acidic soils ofpH ranging from 4.10 - 4.11. There was no major dif-ference in the total soil N with the values rangingbetween 0.14 to 0.17 % for all the four sites. AvailableP levels varied with soils from Kendu bay and PortVictoria having high values ranging between 19.5 –23.00 ppm while soils from Kisumu and Karungu hadlower values ranging from 5 to 10 ppm. Other soilchemical factors varied as follows: Mg (7.60 – 7.85meq % for Kendu bay and Port Victoria and 2.52 –2.76 meq % for Kisumu and Karungu); K (0.19 – 0.20meq % for Kisumu and Karungu and 0.56 – 0.62 meq% for Kendu bay and Port Victoria); Ca (3.50 – 3.95meq % for Kendu bay and Port Victoria and 1.37 –2.48 meq % for Kisumu and Karungu) and Na (0.7meq % for Kendu bay and Karungu and 0.2 - 0.26meq % for Kisumu and Karungu).
3.2 Agronomic performance of bambaragroundnuts
Highly significant (p<0.05) differences were observedbetween landraces BUSB and KAKC in the agronomic
Onyango and Ogolla Fundam Appl Agric 5(2): 176–187, 2020 181
Table 3. Agronomic performance of bambara groundnut landraces grown in four soils of Lake Victoria basin
Site P. Victoria Karungu Kisumu K. bay Mean LSD05% CV%
EDAS KAKC 7.36b 9.32a 9.38a 8.57b 8.66 0.522* 11.7BUSB 7.32c 11.56a 11.92a 8.28b 9.77
DFF KAKC 44.22d 57.23a 63.67a 51.37c 54.12 0.750* 2.8BUSB 51.62c 61.72a 67.74a 54.76b 58.96
LNo14DAS KAKC 8.40a 6.51c 4.40d 8.22b 6.88 0.099* 3.2BUSB 7.68a 5.75b 3.86c 7.58a 6.22
LNo54DAS KAKC 33.17a 26.17c 21.41d 28.51b 27.32 0.434* 3.5BUSB 28.84a 24.74c 19.59c 27.34b 25.13
Ph14DAS (cm) KAKC 6.37a 5.54b 5.27c 5.45b 5.66 0.078* 2.1BUSB 6.21a 5.73b 5.29b 4.08c 5.23
Ph54DAS (cm) KAKC 18.41a 15.56c 15.17c 17.62b 16.69 0.0925* 1.2BUSB 17.27a 14.59c 14.50c 16.72b 15.77
Ph70DAS (cm) KAKC 26.43a 23.72c 22.41d 25.73b 24.57 0.188* 1.7BUSB 25.54a 22.83c 20.43d 24.54b 23.34
Nod21DAS KAKC 2.00b 0.56d 1.56c 3.44a 1.89 0.468* 8.6BUSB 0.67a 0.11b 0.22b 0.67a 0.42
Nod54DAS KAKC 6.89bc 5.90c 5.51d 8.10a 6.6 1.158* 6.5BUSB 4.02d 8.86c 10.61b 12.31a 8.95
DTM (g) KAKC 135.22d 142.44b 145.44a 137.44c 140.14 0.878* 1.3BUSB 144.56c 149.56b 159.22a 144.56c 149.48
S/Pd KAKC 1.44a 1.00b 1.10b 1.39a 1.23 0.164* 2.9BUSB 1.02b 1.11b 1.11b 1.22a 1.12
WHS (g) KAKC 41.22a 36.23c 31.92d 37.82b 36.8 0.434* 2.6BUSB 38.57a 34.58c 30.80d 37.87b 35.46
Means followed by the same letter in a column are not significantly different (* - Significant at p≤0.05) EDAS– Emergence days after sowing; DFF – Days to first flower; LNo14DAS – Leaf number 14 days after sowing;LNo54DAS - Leaf number 54 days after sowing; Ph14DAS – Plant height 14 days after sowing; Ph54DAS –Plant height 54 days after sowing; PH70DS – Plant height 70 days after sowing; Nod21DAS – Nodule number21 days after sowing; Nod54DAS – Nodule number 54 days after sowing; DTM – Days to maturity; S/Pd –Seeds per pod; WHS –Weight of 100 seeds, KAKC – Kakamega Cream landrace; BUSB – Busia Brown landrace.
characters analyzed in screen-house pot experimentsusing the four soil types as shown on Table 3. Theresults showed that Port Victoria and Kendu bay soilswere more suitable for cultivation of bambara ground-nuts than Kisumu and Karungu. The fastest durationto seedling emergence was observed in Port Victo-ria and Kendu bay soils by both landrace KAKCand BUSB which took an average of 7 and 8 daysrespectively (p<0.05). Landrace BUSB took signif-icantly longer duration of 11.56 and 11.92 days toseedling emergence in Kisumu and Karungu soilsrespectively (p<0.05). Plants grown in Port Victoriasoils took the shortest days to form the first flowerwith landrace KAKC taking 44.22 days, followed bythe same landrace in Kendu bay soils taking 51.37days and landrace BUSB which lasted 51.67 days toform the first flowers in Port Victoria soils (p<0.05).The longest duration to form the first flower occurred
in landrace BUSB which lasted 67.74 days in Kisumusoils while landrace KAKC took 63.67 days in thesame soils (p<0.05). Average values of 8 cm in plantheight 14 DAS were observed in both landrace KAKCand BUSB in soils of Port Victoria, significantly differ-ing from the plant height of 4 cm observed in Kisumusoils (p<0.05). Landrace KAKC had the greatest plantheight 54 DAS of 18.41 cm occurring in Port Victoriasoils, followed by the same landrace in Kisumu soilswhich were slightly below 18 cm in height (p<0.05).Kendu bay and Port Victoria soils had above 26 cmhigh plants for landrace KAKC 70 DAS which wasmuch higher than the 22 cm observed in Kisumu soils.
The lowest mean number of leaves per plant 14DAS occurred in Kisumu soils with both landraceshaving an average of 4 leaves plant−1, while the great-est number of leaves (8 plant−1) were observed in lan-drace KAKC planted in Port Victoria soils (p<0.05).
Onyango and Ogolla Fundam Appl Agric 5(2): 176–187, 2020 182
Table 4. Agronomic performance of two soybean varieties grown in four soils of Lake Victoria basin
Site P. Victoria Karungu Kisumu K. bay Mean LSD05% CV%
EDAS SAF 5.19b 4.01c 4.15c 5.5a 4.46 0.165* 6SB19 4.46a 3.48c 3.69b 3.80b 3.86
Ph14DAS (cm) SAF 8.37c 9.34b 9.63b 10.78a 9.53 0.555* 7.6SB19 11.65d 12.41c 13.11a 12.93bc 12.53
Ph35DAS (cm) SAF 26.84b 28.86a 23.82d 24.42c 25.99 0.539* 3SB19 27.61b 32.36a 26.44c 26.87c 28.32
Ph54DAS (cm) SAF 36.33b 45.66a 32.60d 33.71c 37.07 0.464* 3.3SB19 39.73b 49.53a 34.76d 35.87c 39.97
LNo14DAP SAF 10.32b 12.09a 8.01c 7.36d 9.51 0.412* 5.7SB19 12.95b 14.47a 10.12d 10.62c 12.04
LNo35DAS SAF 19.24b 21.41a 14.12d 15.61c 17.59 0.553* 4.3SB19 22.57b 24.65a 17.99d 19.02c 21.06
LNo54DAS SAF 22.41c 26.48a 18.87d 25.82ab 23.39 0.721* 4.4SB19 24.79c 28.46b 21.40d 30.00a 26.16
DFF SAF 42.54c 38.81d 46.73b 52.21a 45.07 0.750* 2.5SB19 39.07c 36.71d 43.91b 54.67a 43.59
Nod21DAS SAF 0.67a 0.00a 0.00a 0.00a 0.17 0.708* 10.8SB19 1.67a 2.00a 1.78a 1.67a 1.78
Nod54DAS SAF 0.67a 0.00a 0.00a 0.00a 0.17 1.129* 5.4SB19 15.86a 9.74b 9.74b 11.09b 11.61
S/Pd SAF 1.80b 2.74a 1.61c 2.60a 2.18 0.142* 8.7SB19 2.70c 2.91a 2.43d 2.77bc 2.7
Means followed by the same letter in a column are not significantly different (* - Significant at p≤0.05) EDAS– Emergence days after sowing; DFF – Days to first flower; LNo14DAS – Leaf number 14 days after sowing;LNo54DAS - Leaf number 54 days after sowing; PH14DAS – Plant height 14 days after sowing; PH35DAS –Plant height 35 days after sowing; PH54DAS – Plant height 54 days after sowing; PH70DAS – Plant height 70days after sowing; Nod21DAS – Nodule number 21 days after sowing; Nod54DAS – Nodule number 54 daysafter sowing; S/Pd – Seeds per pod; KAKC – Kakamega Cream landrace; BUSB – Busia Brown landrace.
When mean leaf number per plant was obtained 54DAS, landrace KAKC outperformed BUSB in all thesoils which obtained the highest number of 33.17leaves plant−1 in Port Victoria soils compared to28.84 for landrace BUSB in the same soil while theleast mean number of leaves 54DAS were obtainedfrom Kisumu soils which gave 19.59 leaves plant−1
(p<0.05). Very few nodules were recovered fromplants of both landraces at 21 DAS with a maximumof 3 nodules obtained from landrace KAKC grownin Kendu bay soils, but this increased to a maximumof 12 nodules 54 DAS from landrace BUSB. In all thesoils, landrace BUSB produced an average of less than2 nodule plant−1 21 DAS since several pots did notform any nodules. Variation was observed in du-ration to maturity with the fastest days attained bylandrace KAKC lasting 137 days in Port Victoria andKendu bay soils different from landrace BUSB whichgave the slowest response of 160 days (p<0.05).
3.3 Agronomic performance of soybeans
Results of agronomic performance of two soybeanvarieties SB19 and ‘Safari’ on soils from four sites inLake Victoria basin are listed on Table 4. The effectof soil type on duration of seedling emergence var-ied significantly (p<0.05) between the two varietiesalthough there was no significant (p>0.001) var×siteinteraction for this variable. The shortest duration toseedling emergence of 3.48 days was observed on Va-riety SB19 on Port Victoria soils, followed by the samevariety on Kendu bay soils at 3.69 days. Variety ‘Sa-fari’ took longer duration for seedling emergence inKisumu and Karungu soils at averages of 5 and 6 daysrespectively (p<0.05). A significant (p<0.05) var×siteinteraction effect was observed on plant height 14DAS with values of 8.37, 9.34, 9.63 and 10.78 cm forVariety ‘Safari’ in Kisumu, Port Victoria, Kendu bayand Karungu soils respectively which differed sig-nificantly with 11.65, 12.14, 13.11 and 12.93 cm forVariety SB19 (p<0.05).
Onyango and Ogolla Fundam Appl Agric 5(2): 176–187, 2020 183
Variety ‘Safari’ had the greatest plant height of28.86 cm at 35 DAS in Port Victoria soils significantly(p<0.05) although it was overtaken by SB19 whichattained the greatest plant height of 49.53 cm at 54DAS in Port Victoria soils; no significant (p>0.001)var×site interactions were observed for this variable.The greatest number of leaves per plant 14 DAS, 35DAS and 54 DAS of 14.47, 24.65 and 28.46 respec-tively occurred in Variety SB19 grown in Port Victoriasoils (p<0.05) while the least number of 7.36, 14.12,and 18.87 cm were found on Variety ‘Safari’ grownin Kendu bay and Karungu soils respectively. Thereoccurred a highly significant (p<0.001) interaction be-tween variety and site of soil sampling for all theplant height factors evaluated. The number of nod-ules at 21DAS on each plant was quite low, with SB19giving the highest value of 2 in Port Victoria soils(p<0.05) compared to 1.67 from both Kisumu andKendu bay soils. Variety ‘Safari’ did not form anynodules in all the soils except Kisumu soils wheresome protuberances occurred in the roots and wererecorded as nodules although the number was neg-ligible. A similar trend occurred on nodule numberplant−1 54DAS in which 15.86, 11.09, and 9.74 nod-ules obtained from Kisumu, Karungu, Port Victoriaand Kendu bay soils respectively for SB19. Highlysignificant (p<0.001) var×site interactions were ob-served for nodules 21 DAS and 54 DAS. There was asignificant difference (p<0.05) in the number of seedsper pod in which a range of 2.43 – 2.79 seeds fromSB19 were obtained in all the soils while a range of1.8 – 2.74 occurred for ‘Safari’ in all the soils.
4 Discussion
The soil type used in cultivation of the two bam-bara groundnut landraces (KAKC and BUSB) andthe plant genotype had a significant effect (p<0.05)on their agronomic performance under screen houseconditions. The sandy loam soils from Port Victoriaand Kendu bay were more suitable for cultivationof bambara groundnuts than the clay loam soils ofKisumu and Karungu. Port Victoria and Kendu bayresulted in faster seedling emergence, shorter days tofirst flower, more leaves per plant and higher shootand root dry weights. Good growth in sandy loamsoil may be attributed to adequate aeration, waterdrainage high water holding capacity that ensuresuitable soil pH (Mojid et al., 1970). Port Victoria andKendu bay soils were moderately acidic with pH 6.1-6.3 compared to the clay loam Kisumu and Karungusoils which were more acidic (pH 4.10 – 4.11). Highersoil pH increases mineralizable of C and N by break-ing the bond organic between constituents and claysmaking N available for plant (Curtin et al., 1998). SoilpH that range from 6 to 8 strongly affects fertilizers’ Nnitrification rates (Kyveryga et al., 2004). Other thanSoil pH effect on soil nutrition, it affects microbial eco-
physical indices such as rhizobia (Blagodatskaya andAnderson, 1998). Soil acidity also hinders availabil-ity of bases such as Ca and Mg and other nutrientssuch as Mo and P which may secondarily influencethe growth and yield of legumes (Swanevelder, 1998;Miller, 2016; Neina, 2019). Where soil is acidic, lim-ing has been recommended to improve production ofbambara groundnuts (CFFRC, 2012; Wijanarko andTaufiq, 2016). Our findings corroborates with those ofLinnemann (1990), Swanevelder (1998) and Berchieet al. (2010) who observed that bambara groundnutplants prefer less acidic soils of approximately pH 6.0.
Kisumu and Karungu soils had lower availableP values (5-10 ppm) compared to Port Victoria andKarungu soils (21-23 ppm), which may have re-sulted in better growth and development in the lattersoil. Soil amendments were not done in this workand thus, low available P status of the Kisumu andKarungu soils must have had a negative impact onthe overall growth performance. Hence, mechanismsfor improving available P levels in the soil is nec-essary, although P-based fertilizers are expensiveand inaccessible to most rural farmers in the region(Ojiem et al., 2006). On the other hand, some studieshave alluded to challenges of direct application ofP-based inorganic fertilizers to the soil since not allof it is usually available to the plants (Okalebo et al.,2002). This offers the alternative of soil amendmentswith the cheaper and more accessible rock phosphate.Rock phosphate has an added advantage of dissolv-ing slowly increasing plant uptake and utilization(Waigwa et al., 2003).
Soil exchangeable cations showed high variabilitywith Kisumu and Karungu soils having lower val-ues of K, Ca, Mg, Mn and Na than Port Victoria andKendu bay soils. In particular, high Na concentrationshave been shown to influence soil salinity. Studies byAmbede et al. (2012) on two bambara groundnut lan-draces under glass house conditions found very highsensitivity to NaCl salinity, in which high concentra-tions significantly decreased percentage germinationand subsequent growth factors. In this study, higherNa concentrations of Port Victoria and Kendu baysoils (0.26 – 0.23 meq %) had a positive effect on plantgrowth, indicating the tolerance of the landraces tothis range of Na concentrations. Landrace KAKCperformed better than landrace BUSB in most of thegrowth factors evaluated. This may be attributed toinherent genetic differences between the landraces.These findings confirmed a preliminary survey con-ducted amongst bambara growing farmers duringseed sourcing, that landrace KAKC is arguably betterin terms of yield enhancing traits. In addition, growthvariations attributable to inherent genetic effects cor-respond to previous studies. Similar genetic effectson bambara plant growth were observed in numberof pods per plant (Ntundu et al., 2006; Adeniji et al.,2008), duration to first flower and plant height (Oue-
Onyango and Ogolla Fundam Appl Agric 5(2): 176–187, 2020 184
draogo et al., 2008), duration to maturity (Berchieet al., 2010), number of nodules per plant and drymatter yield (Adeniji et al., 2008; Mohale and Belane,2013).
Landrace BUSB took relatively longer days toseedling emergence compared to landrace KAKC.This effectively resulted in a longer vegetative periodwhich may also be linked to the lower growth factorsobserved. Landrace BUSB has a brown and thick seedcoat compared to KAKC which has a thin and creamseed coat and this may have affected seedling emer-gence and consequently plant development. Furtherinvestigations on the effect of genetic variations onagro-morphological factors of bambara groundnutsin Lake Victoria soils is necessary. This may provideuseful information to extension officers and breedingprogrammes for higher quality genotypes to farmersin the Lake Victoria basin.
Agronomic performance of soybean varieties ‘Sa-fari’ and SB19 differed remarkably on the four soiltypes. Variety SB19 exhibited faster growth and earlymaturing tendencies in all the four soil types tested.Variety SB19 is a fast maturing soybean line whichwas recommended to farmers in Lake Victoria basinfollowing an up-scaling study by KALRO (Mahasiet al., 2011). As was observed in bambara groundnuts,variations in soil type had a significant influence ongrowth performance of the two varieties; with PortVictoria and Kendu bay soils having better yield com-pared to Kisumu and Karungu soils. This may beattributed to differences in soil pH, available P andexchangeable cations (similar to bambara groundnuttests) and may have resulted due to growth differ-ences in the soybean varieties. Soil pH has been asso-ciated with plant intake of molybdenum which has adirect influence in legume nodulation (Somesegaranand J., 1985). Molybdenum concentration was notanalysed in the soil samples used in this study buta report by Motsara and Roy (2008) indicates thatplants grown at pH values above 6.4 access the min-eral more easily than plants grown in highly acidicsoils (below pH 5.5). Molybdenum is also criticalfor nodule formation and nitrogen fixation (Some-segaran and J., 1985). It is therefore plausible to inferthat the more acidic Kisumu and Karungu soils in-hibited intake of this mineral element resulting in thelow number of nodules observed and may have hada negative effect in overall plant growth.
Differences in agronomic performance betweenVariety SB19 and ‘Safari’ may be attributed to chemi-cal of soils on which they were cultivated. However,growth variation due to genetic/varietal differenceswas evidenced by better growth of Variety SB19. Itshowed early maturing tendencies resulting in betterseedling emergence, faster duration to flower forma-tion, earlier pod setting and faster maturity. VarietySB19 was previously reported to be an early matur-ing variety by Waswa (2013) and Mahasi et al. (2011).
It was recommended as a suitable soybean line forcultivation in Lake Victoria basin since the region ex-periences erratic rainfall which may insufficient forslow growing varieties. Variety SB19 had high meannodule numbers in nearly all the soils, most of whichwere effective. This was unlike Variety ‘Safari’ whichproduced two nodules in Kisumu soils. Being spe-cific, the variety may have secluded many rhizobialgroups, which led to low nodulation that may haveslowed its growth. Soil chemical analysis revealedlow levels of N in all soils (0.14-0.17%) as was shownby the soil analysis. Effectively nodulated legumeplants use both N-fixed due to symbiosis and soil Nfor its growth and metabolism (2008, Unkovich, M.and Herridge, D. and Peoples, M. and Cadisch, G.and Boddey, R. and Giller, K. and Chalk, P.). At thesame time, since symbiotic N-fixation is directly de-pendent on translocation of carbohydrates from theleaves, the rate of fixation is fully synchronized withthe rate of plant growth (Sessitsch et al., 2002). How-ever, non-nodulated/ineffectively nodulated plantsare completely dependent on soil N for its growth(Giller, 2001) and this may explain the slow growthobserved in Variety ‘Safari’.
5 Conclusion
Agronomic performance of bambara groundnutsand soybeans was influenced by the soil type withPort Victoria and Kendu bay soils resulting in bet-ter growth compared to Kisumu and Karungu soils.Soil chemical properties and inherent varietal differ-ences between the legumes significantly influencedplant growth and distribution of rhizobial isolatesobtained from each site. Although sensitive to low Pand pH, bambara groundnuts and soybeans are likelyto perform well in the region with proper soil amend-ments. This study revealed that soybeans and bam-bara groundnuts require soils of high P and near neu-tral pH for optimum agronomic performance. Guide-lines on soil amendments through liming and use ofrock phosphate as a P-source may lead to improvedproduction of the two legumes in Lake Victoria basin.Landrace KAKC and SB19 were found to have betteragronomic performers and are recommended to farm-ers and seed companies for certified seed production.
Conflict of Interest
The authors declare that there is no conflict of inter-ests regarding the publication of this paper.
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